The objectives of the present study are: 1) to quantify and qualify the population of efferent (sympathetic) axons entering the apical foramina of rat molar teeth and to quantify and qualify the population of afferent (somatic) axons entering the apical foramina of rat molar teeth, 3) to document the location, distribution and mode of termination of the afferent (somatic) nerve terminals throughout the dental pulp, 4) to document the location, distribution and mode of termination of the efferent (sympathetic) nerve terminals throughout the dental pulp. Relationships between nerve fibers, odontoblasts, and fibroblasts will be analyzed in an effort to determine the functional roles that these neural elements may play in dental sensation and dentinogenesis. In the first series of experiments, the tracer horseradish peroxidase (HRP) will be injected into either the trigeminal or superior cervical ganglia of adult rats. The enzyme will be endocytosed by the ganglion cell bodies and transported intraxonally to the tooth pulp nerve terminals. The HRP-labled tooth pulp nerve endings will be identified at the electron microscopic level and analyzed critically with reference to their respective origins, ultrastructures, numbers, modes of termination and peripheral distribution. In the second series of experiments, detailed light and EM studies of the normal rat tooth pulps will be performed to supplement the experimental HRP studies described above. The results of the present study should increase significantly our understanding of the nature and sources of tooth pulp innervation. The long range goal is to correlate this structural information with functional studies in order to increase our understanding of the peripheral neural mechanisms within the dental pulp and their possible roles relative to pain and dentinogenesis.